In an engine driven vehicle such as a motorcycle, a generation device is provided that outputs a DC voltage controlled so as not to exceed a set value using a magnetic AC generator driven by an engine as a power supply, and power is supplied from this generation device to a load including a battery.
Unlike an excitation AC generator, the magnetic AC generator cannot control a magnetic field, and thus a short circuit type regulator has been used that short-circuits an output of a generator via an output short-circuit switch when the output of the generator becomes excessive. When using the short circuit type regulator, however, a large current flows through the output short-circuit switch at the time of voltage adjustment to generate a large amount of heat in the output short-circuit switch, and thus a large heatsink needs to be provided to cool the output short-circuit switch, thereby increasing the size of a control device. Also, an output short-circuit switch having a large current capacity needs to be used, thereby increasing costs of the control device.
Thus, as disclosed in Japanese Patent Application Laid-Open Publication No. 11-46456, a control device provided in a generation device that supplies power to a load including voltage accumulation means such as a battery with a rectification output of an AC generator has been proposed in which a circuit for applying an AC control voltage having the same frequency as an output of the generator from the load to an armature winding of the generator is provided, and a phase of the AC control voltage is controlled to adjust an output voltage.
The proposed control device is comprised of a rectifier circuit that has a plurality of input terminals to which an output of the armature winding of the AC generator is input and a pair of output terminals connected across the voltage accumulation means, converts an AC voltage input to the input terminals into a DC voltage, and outputs the DC voltage from the output terminals; an inverter circuit having DC terminals and AC terminals connected to the output terminals and the input terminals of the rectifier circuit; and inverter control means. The inverter control means controls the inverter circuit to convert a voltage across the voltage accumulation means connected across the output terminals of the rectifier circuit into an AC voltage having the same number of phases and the same frequency as the output of the generator, and apply an AC control voltage having a phase adjusted to maintain the output voltage of the rectifier circuit at a target value from the AC terminals to the armature winding.
Providing the circuit that applies the AC control voltage to the armature winding to control the phase of the AC control voltage as described above basically allows the output of the generator to be increased by delaying the phase of the AC control voltage and reduced by advancing the phase of the AC control voltage.
Thus, the phase of the AC control voltage is controlled according to a deviation between the output voltage and the target value so that the phase of the AC control voltage is delayed when the output voltage is lower than the target value, and the phase of the AC control voltage is advanced when the output voltage is higher than the target value, thereby controlling the output voltage to be maintained at the target value. The amount of change in the generator output when the phase of the AC control voltage is changed can be adjusted as required by changing a mean value of the AC control voltage such as by PWM control of switch elements of the inverter circuit.
In the specification, such control is referred to as “vector control” in a sense that a vector (magnitude and phase) of the AC control voltage applied to the armature winding of the generator is controlled to control the generator output.
When the vector control as described above is performed in the magnetic AC generator, delaying the phase of the AC control voltage allows an output current of the generation device to be increased more than in the case without performing the vector control (the case where the generator output is simply provided to the load via the rectifier circuit) in a low rotational speed area of the generator, but delaying the phase of the AC control voltage does not allow the output current to be increased in middle and high rotational speed areas. If the phase of the AC control voltage is excessively delayed, the output current of the generator may be reduced more than in the case without performing the vector control even in any rotational speed area.
In order to prevent an area in which the output current of the generator is reduced from being created by the excessively delayed phase of the AC control voltage, a phase of the AC control voltage in which a maximum output current can be obtained has been previously stored in a memory of a controller as a maximum output current phase (a fixed value) to control the phase of the AC control voltage so as not to be further delayed with respect to the maximum output current phase.
The maximum output current phase, however, actually changes according to conditions such as the temperature of the generator. Thus, if the maximum output current phase is the fixed value, the phase of the AC control voltage may be excessively delayed to prevent proper control when the condition such as the temperature of the generator changes, thereby reducing the output current of the generator more than in the case without performing the vector control.